A busy worker sent in for a truant (8)
I believe the answer is:
absentee
'a truant' is the definition.
(I've seen this before)
'a busy worker sent in' is the wordplay.
'busy worker' becomes 'bee' (I've seen this in another clue).
'in' means one lot of letters goes inside another.
'bee' enclosing 'sent' is 'bsentee'.
'a'+'bsentee'='ABSENTEE'
'for' acts as a link.
(Other definitions for absentee that I've seen before include "skiver" , "one's failed to show up" , "to prompt a hearty increase in affection!" , "One who stays away" , "He's not here!" .)